1. Field of the Invention
The present invention relates to a liquid application mechanism and an inkjet recording apparatus.
2. Description of the Related Art
In the technical field of inkjet recording, in order to improve the quality of recording using ink including a coloring material such as a pigment, a technique of applying process liquid, which promotes aggregation of the pigment, to a recording medium (recording paper) has been proposed. When ink including a pigment is ejected onto a recording medium that has been treated with the process liquid, the pigment is insolubilized, so that the density of recording can be improved and bleeding can be reduced or prevented. As a result, the quality of recording is improved.
Japanese Patent Laid-Open No. 2007-44649, for example, discloses a liquid application mechanism for applying process liquid to a recording medium. This publication discloses a mechanism including an application member including an application roller for applying application liquid to a recording medium, a liquid holding member for holding the application liquid between the liquid holding member and the application member, a storage unit for storing the application liquid, a pump for circulating the application liquid, and a channel through which the application liquid flows between the storage unit and the application member. A supply port is disposed at one end of the liquid holding member so that the application liquid can be supplied from the storage tank to the liquid holding member. A recovery port is disposed at the other end of the liquid holding member so that the application liquid can be recovered to the storage unit.
In the liquid application mechanism, foreign substances on a recording medium or foreign substances generated by friction between the application member (application roller) and a recording medium (for example, paper powder) may be transported together with the application liquid that is recovered via the application member and the liquid holding member, and the foreign substances may enter the application liquid stored in the storage unit. If the application liquid including the foreign substances circulates through a channel or other members, the foreign substances may block the channel and may impair circulation, a recording medium to which the application liquid is applied may be soiled with the foreign substances, or the foreign substances on the recording medium may adhere to a conveying unit and the precision of conveyance may decrease.
While the application liquid does not circulate in the liquid application mechanism, the foreign substances in the application liquid in the storage unit settle due to gravitation and are deposited on the bottom surface of the storage unit. At this time, the application liquid and the foreign substances are separated from each other. However, when circulation of the application liquid is restarted, the foreign substances that have been deposited on the bottom surface are raised and mixed into the application liquid. In order to suppress this phenomenon, the liquid application apparatus disclosed in Japanese Patent Laid-Open No. 2007-44649 includes a trap space section in a storage unit for storing liquid, the trap space section having an opening below an outlet for supplying the liquid to a liquid holding member. While liquid is circulating or is not circulating, the foreign substances are guided into the trap space section through the opening, and the foreign substances are removed from the liquid.
Japanese Patent Laid-Open No. 2004-130614 discloses a technology for preventing foreign substances from being circulated in a liquid application mechanism so that the function of the liquid application mechanism may not be impaired due to entry of the foreign substances into the application liquid. With this technology, liquid including foreign substances that have entered a circulation channel from the outside is filtered using a filter so as to remove the foreign substances from the liquid.
However, with the apparatus disclosed in Japanese Patent Laid-Open No. 2007-44649, which includes the trap space section disposed at the bottom of the storage unit, although the foreign substances that enter through the opening of the trap space section can be trapped, the foreign substances that have been deposited on portions excluding the opening of the trap space section cannot be trapped in the trap space section. Therefore, the foreign substances that have not been trapped in the trap space section may reenter the liquid when the liquid circulates.
With the technology disclosed in Japanese Patent Laid-Open No. 2004-130614, which removes foreign substances using a filter, the filter may become clogged over time, whereby the performance of removing the foreign substances may be impaired and the flow resistance when liquid circulates may increase. In particular, this problem is significant when a fine-pitched filter is used so as to improve the performance of removing the foreign substances. Therefore, the filter has to be frequently replaced or cleaned, which requires manpower.